I'm one of the people who used to work in print, therefore at the time, I had to buy the $80 PANTONE swatch book. The book let me try to come up with the closest color in CMYK printing to the actual color in the real world. It's not trivial; 7Up was a client of ours back in the ad agency days, and "7Up green" would absolutely no reproduce accurately, not without a 5th plate and a lot of trapping and stripping and the execs at 7Up wouldn't pay for it.
Today, PANTONE is owned by the very smart and aggressive X-Rite company, and one of their innovations/offerings is an online color spec widget. You use a color field and hue slider (shades of Xara) to specify a color, hit the Submit button and the widget offers several close matches in the PANTONE Color Management system.
Free PANTONE online conversion widget
Hey, it's worth a trip just to play with the thing. I came very close to the colour I sought when I looked at the samples on my screen, and then at the physical swatch book. BTW, you need a fairly well calibrated monitor and viewing conditions to make your matches a little more accurate. When I say this, understand that screen colours are in the additive color model RGB, while inks, CMYK are subtractive colours, so matching perfectly between two opposing colour models is a little like trying to drive a boat on a highway.
But it's the best system we have, I feel.
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